1. Field of the Invention
This invention relates to a scanning type image displaying apparatus, and particularly to an image displaying apparatus suitable, for example, for a head-mounted-display apparatus (HMD) or the like.
2. Description of the Related Art
At present, as a display element used in an HMD, there has been proposed one using a transmission type liquid crystal display element, a reflection type liquid crystal display element, an EL element or the like. These elements, however, require all pixels necessary for display to be installed therein and therefore, a pixel defect is liable to occur and the price of the element itself becomes very high.
In contrast, there has been disclosed and proposed a displaying apparatus for displaying an image by the use of not a two dimensional image display element such as a liquid crystal display element or an EL element, but a light source emitting a linear beam and a scanning member (scanner) for scanning the beam. U.S. Pat. No. 5,467,104 discloses a technique of scanning with lights of three colors, i.e., red (R), green (G) and blue (B), in a horizontal direction and a vertical direction, and directly forming an image on a retina through an optical system.
In the scanning type image displaying apparatus disclosed in the above-mentioned U.S. Pat. No. 5,467,104, however, it is required to scan with the lights at a very high speed and therefore, a very small device is used as a scanning member such as a mirror for scanning with the lights. Accordingly, there is the problem that a scanning light beam is a very thin one and the diameter of the light beam at an observer's pupil position becomes very small.
As a method of enlarging such a small emergence pupil diameter, there is a technique disclosed in U.S. Pat. No. 5,701,132. In U.S. Pat. No. 5,701,132, there is disclosed a configuration in which a surface to be scanned such as a lens array or a diffusing plate is scanned with modulated beam by a scanning member to thereby form an image, and the image to be transmitted through the surface to be scanned and observed is presented to an observer.
Also, Japanese Patent Application Laid-open No. H11-84291 discloses a configuration in which light from a light source is passed through a polygon-mirror-shaped deflector, whereafter an intermediate image is formed by the use of a free curved surface prism, and the intermediate image is directed to an observer by the use of a free curved surface prism.
Japanese Patent Application Laid-open No. 2001-4955 and Japanese Patent Application Laid-open No. 2001-194617 propose a relatively compact optical system for making light from a light source into a somewhat thick beam by the use of an eccentric free curved surface optical system, reflecting the beam by a scanning member and directing it to an eyeball.
When in order to use a small-diameter beam and yet enlarge the emergence pupil, use is made of the construction disclosed in U.S. Pat. No. 5,701,132, an intermediate image transmitting type surface to be scanned is used, and this leads to the problem that an optical path becomes long and the apparatus becomes bulky. On the other hand, if the diameter of the beam incident on the scanning member is made large to thereby make an emergence pupil large, the aberration correction of an intermediate image formed on the surface to be scanned through the scanning member becomes difficult and therefore, the realization of high optical performance becomes difficult and the size of an optical system is increased. Also, a large scanning member becomes necessary, and this leads to the problem that the apparatus becomes bulky and electric power required for scanning is increased.